Vertical metal-semiconductor microresonator photodetecting device and production method thereof

ABSTRACT

Device for photodetection with a vertical metal semiconductor microresonator and procedure for the manufacture of this device. 
     According to the invention, in order to detect an incident light, at least one element is formed over an insulating layer ( 2 ) that does not absorb this light, including a semiconductor material ( 6 ) and at least two electrodes ( 4 ) holding the element, with the element and electrode unit being suitable for absorbing this light and designed to incease the light intensity with respect to the incident light, in particular by making a surface plasmon mode resonate between the unit interfaces with the layer and the propagation medium for the incident light, with the resonance of this mode taking place in teh interface between the element and atleast one of the electrodes, with this mode being excited by the component of the magnetic field of the light, parallel to the electrodes. Application for optical telecommunications.

TECHNICAL FIELD

The present invention concerns a photodetection device as well as aprocedure for the manufacture of this device.

As will be seen better as follows, the device that is the objective ofthe present invention offers a wide range of selection for the wavelength, extreme speed and great sensitivity.

It is applicable to any field liable to take advantage of at least oneof these qualities such as, for example, the microscopic detection ofmolecules and, more specifically, very high speed opticaltelecommunications, greater than or equal to 100 Gbits per second.

PRIOR STATE OF THE ART

MSM (Metal-Semiconductor-Metal) type photodetectors are generally quitesimple to manufacture, they are easily fitted into field effecttransistors and allow relatively high speed to be obtained but to thedetriment of performance. Hereinafter, some MSM photodetectors areconsidered that are known as well as their drawbacks.

In a known photodetector based on InGaAs, whose distance between theelectrodes is 1 μm, the transit time of the holes is around 10 ps, whichcorresponds to a cut-off frequency of less than 20 GHz. Therefore thedistance between the electrodes must be reduced in order to cut down thetransit time for the holes. When the distance between the electrodesdrops below 0.1 μm, the transport can no longer be considered asstationary. The transit time then becomes much lower than 1 ps.

The masking of the active zone by the electrodes is one of the maindrawbacks of the known MSM structures and limits their quantum yield.Furthermore, because of the limited absorption of the materials used inthese structures (the length of absorption is greater than 1 μm), thethickness of the absorption zone must be limited so as to prevent thecreation of charge carriers far away from the electrodes. The quantumefficiency of the known photodetectors, since they have a range betweenthe electrodes of less than 0.1 μm, is therefore extremely bad.

On the contrary, the known MSM structures, whose external quantum yieldis good, have a low speed.

But nowadays a super-fast photodetector (whose response time is lessthan 1 ps) is a crucial element for very high speed opticaltelecommunications (100 Gbits/s and above). The performance levelssought include great sensitivity and broadband, at wavelengths between1.3 μm and 1.55 μm. Whatever type of photodetector it may be (P(I)Ndiode or Metal-Semiconductor-Metal structure), the target of high speedforces the distance between the electrodes to be short (less than 100nm) and that the light to be detected must be absorbed in a minimumvolume.

Hence, the bulk InGaAs semiconductor has a characteristic absorptionlength of around 3 μm at a wavelength of 1.55 μm.

In the PIN diodes and in the MSM structures, the reduction of thetransit time for the charge carriers is directly linked to a drop in theexternal quantum yield.

The design of the known photodetectors therefore is necessarily thesubject of a compromise between yield and speed.

OVERVIEW OF THE INVENTION

The device that is the subject of the invention aims to radicallyquestion this compromise and uses a vertical microresonator, whichallows, for example, a quantum yield of over 70% to be attained in a lowcapacity structure, whose range between the electrodes may be less than50 nm and may lead to a bandwidth of over 1 THz.

The principle for a device in accordance with the invention consists ofconcentrating the light that we may wish to detect in a resonant manner,in a low volume MSM type structure, by using the fast drop in evanescentmodes excited in the Metal/Semiconductor interface.

The surface plasmon modes allow this aim to be achieved.

Unlike the known structures, the plasmons do not spread horizontally(that is to say in parallel to the substratum of the structure), butrather they remain confined along the vertical surface of the electrodesin the structure.

In a precise manner, the aim of the present invention is aphotodetection device intended to detect an incident light with apredefined wavelength, propagating in a propagation medium, with thisdevice being characterised by the fact that it includes an electricallyinsulating layer that does not absorb this light and, on this layer, atleast one element, including a semiconductor material, and at least twobiasing electrodes, intended to be carried respectively to potentialsthat are different from one another, with the electrodes surrounding theelement, with the set formed by the element and the electrodes beingadapted to absorb the incident light (in other words, the element and/orthe electrodes are suitable for absorbing this light), with the elementand the electrodes having a shape that is substantially parallelepipedaland extending following the same direction, with the dimmensions of theelectrodes and the element, counted transversally to this direction,being chosen according to the predefined wavelength, in such a way as toincrease the light intensity in the set formed by the element and theelectrodes with respect to the incident light, by making at least one oftwo modes resonate, that is to say a first mode which is a surfaceplasmon mode and which made to resonate between the interfaces that thisset includes with the insulating layer and the propagation medium, withthe resonance of this first mode taking place at the interface betweenthe element and at least one of the electrodes, with this first modebeing excited by the component of the magnetic field associated with theincident light, a component that is parallel to the electrodes, and asecond mode which is a transverse electrical mode of an opticalwaveguide which is perpendicular to the insulating layer and includesthe two electrodes, with this second mode being excited by the componentof the electric field associated with the incident light, a componentwhich is parallel to the electrodes.

Preferentially, when the surface plasmon mode is made to resonate, thewidth of each element, counted perpendicularly to the direction of theelectrodes, is less than λ and greater than 0.02×λ, where λ is thewavelength of the incident light and the thickness of each element isless than λ/(2n), where n is the average refractive index for eachelement.

According to a first particular form for building the device that is thesubject of the invention, the electrodes are made of the sameelectrically conductive material and are the same height, countedperpendicularly to the insulating layer.

According to a second particular form for building it, the electrodeshave at least one of the following two properties (a) they are made ofdifferent electrically conductive materials and (b) they have differentheights, counted perpendicularly to the insulating layer, in such a waythat the resonance takes place essentially on the side of the electrodewhich collects the slow charge carriers at the time of the biasing ofthe electrodes.

The element that the device carries may include a semiconductorheterostructure.

According to a particular mode for its construction, the device that isthe subject of the invention includes several elements and electrodesthat alternate on the insulating layer, with each electrode being madeof a single metal or of two different metals.

In this case, in a first particular mode for its implementation, theelectrodes are intended to be carried to potentials which grow from oneend electrode to the other end electrode in the set of electrodes.

The device that is the subject of the invention may then also include aresistive material, for stabilising potentials, which is in contact withthe electrodes and runs from one end electrode to the other endelectrode in the set of electrodes. The latter allows the set ofelements to be polarised under a high voltage.

In a second particular mode for its implementation, the electrodes areintended to be carried to potentials whose absolute values are equal andwhose signs alternate.

According to a preferred mode for the implementation of the device thatis the subject of the invention, this device also includes a means forreflection planned to reflect the light that is not absorbed, crossingthe insulating layer, with the thickness of this insulating layer beingchosen so that the light reflected by the means for reflection will bein phase with the light waves present in the set formed by each elementand the electrodes and will participate in the resonance.

In a first example, the device that is the subject of the invention isintended to detect an incident light whose wavelength is approximately0.8 μm, this device is formed on a substratum of GaAs, the element ismade of GaAs, the electrodes are made of Ag, the insulating layer ismade of AlAs, or out of an Al_(x)Ga_(1-x)As material, with x beingchosen in such a way that this material will not absorb the incidentlight but will allow a selective etching of the GaAs, and the reflectionmeans is a multiple layer AlAs/AlGaAs mirror.

In a second example, the device is intended to detect an incident lightwhose wavelength is approximately 1.55 μm, this device is formed on asubstratum made of InP, the element is made of InGaAs, the electrodesare made of Ag, the insulating layer is made of AlInAs and the means forreflection is a multiple layer mirror made of GaInAsP/InP orAlGaInAs/AlInAs. As a variation, the device is formed on a GaAssubstrate, with the element being made of an InGaAsNSb alloy, theelectrodes are made of Ag, the insulating layer is made of AlAs, or inan Al_(x)Ga_(1-x)As material, with x being chosen in such a way thatthis material will not absorb the incident light but will allow aselective etching of the GaAs, and the reflection means is a multiplelayer GaAs/AlAs mirror.

In a third example, the device is intended to detect an incident lightwhose wavelength belongs to the infrared range, and the electrodes aremainly made of Ag or Au in order to absorb the incident light, with theelement not absorbing this incident light.

According to a first particular mode for implementing the invention, thepropagation medium is air.

According to a second particular mode for implementation, thepropagation medium is a light guide parallel to the direction in whichthe electrodes from each element spread out.

The present invention also concerns a procedure for manufacturing thedevice that is the subject of the invention, in which a given thicknessof the semiconductor material for the element is made to grow on theinsulating material, this semiconductor material is etched selectivelyin order to remove from it portions in the sites corresponding to theelectrodes and these electrodes are formed on these sites.

According to a first particular mode for implementing the procedure thatis the subject of the invention, the same mask is used to selectivelyetch the element and then to form the electrodes.

According to a second particular mode for implementing the procedurethat is the subject of the invention, a mask is used to selectively etchthe element, this mask is removed, the electrodes are formed using atleast one metal and the excess material from this metal is removed bymeans of mechanical or mechanical-chemical polishing.

In this case, according to a particular mode for implementing theinvention, the excess metal is removed by means of a selectivemechanical or mechanical-chemical polishing of the metal with respect tothe element, with this element being made up by a material whosehardness is great compared to that of the metal.

According to a particular mode for implementation, the element includesan upper layer and the excess metal is removed by means of a selectivemechanical or mechanical-chemical polishing of the metal with respect tothe element, with the upper layer of the element being made up by amaterial whose hardness is great compared to that of the metal.

Two metals may also be used in order to form the electrodes anddeposited successively in an oblique manner with respect to theinsulating layer.

It should be noted that, in the present invention, the use of a largenumber of elements amongst which some electrodes are deposited, insteadof the use of a single element placed between two electrodes, allows anetwork to be built whose electromagnetic modelling is very muchsimpler.

Then it may be shown that the first mode is made to resonate, whichcorresponds to some vertical plasmons that are weakly coupled two bytwo.

The lower and upper ends of the vertical sides of the electrodes have amirror effect on the plasmons in the metal-semiconductor interface,which allows a Fabry-Pérot type of resonance to be established and soabsorb the largest part of the TM (transverse magnetic) polarisedincident wave.

The modelling has also allowed the same Fabry-Pérot type resonancephenomenon to be demonstrated for the TE (tranverse electrical) modes ofthe flat wave guide formed between two electrodes separated by anelement and so absorb the largest part of the TE polarised incidentlight for some suitably chosen parameters of the device.

In the case of TM polarisation and in the case of TE polarisation, totalabsorption may be obtained by using a Bragg mirror under the electrodesto reflect the wave transmitted in the insulating layer.

The figures for the drawings attached herewith show that, unlike theexcitation of horizontal surface plasmons (that is to say those parallelto the insulating layer), the resonance is barely sensitive to theinclination of the incident light wave that we want to detect. It istherefore possible to focus the light wave strongly onto the device andto only activate a small number of elements (for example, 3 to 5),whilst reducing the quantum yield of the device by very little (withrespect to the case in which a large number of elements are used).

Furthermore, in the case of TM polarisation, it is recommended that thethickness of each element should be produced accurately whilst that isnot the case for the transversal dimensions of each element and of theelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention shall be better understood after reading thedescription of the examples for the implementation provided below,purely for information purposes and not at all limited thereto, byreferring to the drawings attached herewith, on which:

FIG. 1 is a schematic and partial perspective view of a device inaccordance with the invention,

FIGS. 2 and 3 are schematic and partial cross-sections of other devicesin accordance with the invention,

FIG. 4 shows the variations in the reflective index according to theangle of incidence for the light to be detected, for two differentvalues of the network height formed by the elements and the electrodesfrom a device in accordance with the invention,

FIG. 5 shows the variations in the reflective index according to thisheight, in a device in accordance with the invention,

FIGS. 6A to 6E illustrate in a diagram form some variations for thisprocedure, and

FIGS. 6F to 6H illustrate in a diagram form the stages of a procedurefor manufacturing a device in accordance with the invention,

FIG. 7 is a diagram side view of another device in accordance with theinvention.

DETAILED DESCRIPTION OF THE PARTICULAR MODES FOR IMPLEMENTATION

A device in accordance with the invention is to be seen from a diagramtype and partial perspective on FIG. 1. It involves a structure forminga network of metal-semiconductor-metal detectors, also abbreviated asMSM, which is set out on an electrically insulating layer 2.

This network is a set of metal electrodes 4 which alternate with somesemiconductor elements 6.

These electrodes and these elements have an approximatelyparallelepipedal shape and spread out following the same direction D onthe layer 2.

In the example in FIG. 1, there are several semiconductor elements. In avariation that is not shown, a single semiconductor element is used 6set out between two electrodes 4.

Another device in accordance with the invention is seen as a schematicand partial transversal cross-section view in FIG. 2. This device inFIG. 2 is identical to the one in FIG. 1 apart from the fact that italso includes a multiple layer mirror 8 also called a Bragg mirror.

This multiple layer mirror is an alternating stack of layers ofmaterials that do not absorb light, with different refractive indicesn_(A) and n_(B). The respective thicknesses h_(A) and h_(B) of theselayers are calculated according to the range of wavelengths to bereflected.

It may also be seen that the device in FIG. 2 is formed on a substratum9. The mirror 8 is built between this substratum and the layer 2.

The device in FIG. 2 (and therefore the device in FIG. 1) may be brokendown into three zones, I, II and III.

As follows, it is assumed that the incident light wave 10 that we wantto detect with the device reaches the latter through zone I made up byair.

The case of a device according to the invention may be described in asimilar manner which is placed in contact with a light wave guide inwhich a light to be detected with the device is propagated. This case isillustrated in a diagram and partial form in FIG. 3 where the guide hasreference 12. This guide 12 stretches out following the direction D andthen in parallel to the electrodes 4 and the semiconductor elements 6.

Going back to FIG. 2, zone II is made up by the network of the metalelectrodes 4 having a transversal cross-section that is approximatelyrectangular and the elements 6 made up by a semiconductor that absorbsthe incident light, with the wavelength of this light being known.

In a variation which is not shown, each element 6 is made up by a layerof a semiconductor material which absorbs the incident light and adielectric layer which lines this layer of semiconductor material.

Zone III corresponds to the layer 2 which is made up by a non-absorbentsemiconductor in a mesh layout with the semiconductor in zone II. Thiszone III may, as has been seen, include a Bragg mirror which reflectsthe light waves transmitted from zone II to zone III.

The incident light to be detected 10 that may be broken down intopolarised TM light and into polarised TE light, reaches the structurethrough zone I. The polarised TM light excites the surface plasmon modesalong the interface between the metal and the semiconductor in zone II.The waves corresponding to these modes are then reflected to theinterfaces in zones II/III and II/I.

This resonance phenomenon for a TM polarisation is shown in a diagramform in FIG. 2 where the resonant surface plasmons 14 have beensymbolised.

The height h_(m) between the II/III interface and the Bragg mirror 8 iscalculated in such a way that the wave transmitted from zone II to zoneIII and reflected by this mirror 8 is in phase with the waves (plasmons)in the medium II and participates in the resonance.

The TE polarised light excites the modes of the flat wave guide betweentwo electrodes 4. These modes are also reflected to the II/III and II/Iinterfaces and the waves transmitted in zone II are reflected by theBragg mirror 8.

The working of the device is then similar to that of a classic MSMstructure.

Some potentials are applied respectively to the electrodes (by biasingmeans that are not shown), these potentials can continue to grow fromone electrode to the next (biasing in a progressive manner) or thesepotentials may be equal in absolute values but have signs whichalternate when changing from one electrode to the other.

In the semiconductor in zone II, the absorption of the light istranslated by the creation of an electron-hole pair for each photonabsorbed (whose energy is greater than the prohibited bandwidth or gapin the semiconductor). Under the effect of the electrical field, theelectron is then attracted by that of the two electrodes closest to theelectron, which has the highest potential and the hole by that of thesetwo electrodes which has the lowest potential. This movement of thecharges creates an electrical current in the electrodes.

The speed of the photodetector response depends on the distances betweenthe electrodes and the potentials to which these electrodes are carried.

It should be noted that part of the incident light wave can be absorbedin the metal from which the electrodes are made. This absorptionparticipates partially in the creation of carriers in the semiconductorelements 6: the excited electrons may pass over the potential barrier orelse pass through a tunnel effect.

The different materials (metal for the electrodes, absorbent andnon-absorbent semiconductors) are chosen according to the wavelength ofthe incident wave to be absorbed. For example, the metal electrodes maybe made of silver, a metal whose reflective index (for bulk Ag) is highand which therefore allows a strong resonance to be obtained. Gold,platinum, aluminium or any other highly reflective metal may also beused. It should also be noted that the electrodes may be made up by twometals, for the reasons that will be examined later.

For an absorption of around 0.8 μm, GaAs is selected as the absorbentsemiconductor and AlAs as the non-absorbent semiconductor (or, insteadof AlAs, an Al_(x)Ga_(1-x)As material, with x being chosen in such a waythat this material will not absorb the light for which the wavelength ispredefined, but will allow a selective etching of the GaAs) and theBragg mirror is formed by AlAs and Al_(0,2)Ga_(0,47)As. For anabsorption of around 1.55 μm, In_(0,53)Ga_(0,47)As is chosen as anabsorbent semiconductor and InP as a non-absorbent semiconductor and theBragg mirror is formed by GaInAsp/InP or by AlGaInAs/AlInAs.

On the other hand, the different parameters of the device e (width ofthe electrodes), d (pitch of the network) and h (height of the network,that is to say the thickness of the electrodes and of the semiconductorelements) as well as the thickness h_(m) of the insulating layer 2, seeFIG. 2, are adjusted in such a way as to excite either the surfaceplasmons for the TM polarisation or the TE modes, and in such a way asto obtain Fabry-Pérot resonance for these modes. It is also possible tochoose these parameters so as to excite both types of modessimultaneously in an optimum manner.

It is preferentially required that the distance d-e between two adjacentelectrodes (that is to say the width of each element) should rangebetween λ and 0.02×λ, where λ is the wavelength of the light to bedetected and that h is less than λ/(2n), where n is the averagerefractive index of the elements 6. Thus a device is obtained with a lowtransit time and low capacity.

By way of an example, a number N of elements may be used, with 2≦N≦20,with the pitch d being included between 0.1×λ and 1×λ.

At λ=0.8 μm and with the materials given above, total absorption isobtained (over 99%) for the TM polarised incident wave when choosing anetwork step of d=150 nm, an overlap rate (r=e/d) of r=0.5 (50%), anetwork height h of 55 nm and a Bragg mirror made up by 20 layers. Theenergy absorbed by the semiconductor in zone II is around 74%, with theremainder (26%) being absorbed by the metal.

The TE polarised incident wave is also totally absorbed when choosingd=150 nm, r=0.4 and h=305 nm. For a non-polarised wave, the choice ofthe parameters d=150 nm, r=0.5 and h=210 nm allows a reflection of theincident wave of 16% to be obtained and an absorption in thesemiconductor of around 72%.

The curves in FIGS. 4 and 5 allow the yields of the devices that meetthe invention to be characterised.

FIG. 4 shows the variations in the reflective rate T (in %) which is theratio of the light intensity reflected by the device to the incidentlight intensity on this device versus on the incidence angle θ (inradians) that may be seen on FIG. 2, for the following values of theparameters: d=0.15 μm, r=0.5 and h=53 nm for curve I whilst it is h=55nm for curve II.

FIG. 5 shows the variations in the reflective rate T (in %) versus theheight h of the network (in μm) for d=0.15 μm, r=0.5 and θ=0° (normalincidence).

The manufacture of a device in accordance with the invention, forexample the device in FIG. 2, is performed in five stages which areshown in a diagram form on FIGS. 6A to 6E.

The layers 16 and 18 of the Bragg mirror, the layer 2 made of AlAs andthe layer 22 made of GaAs which is on top of layer 2 (FIG. 6A) are madeby means of epitaxy (for example, using molecular jet epitaxy) on asubstratum 9 made of GaAs then an electronic masking of the networkpatterns (FIG. 6B) is made. Thus the zones corresponding to theelectrodes are defined thanks to the deposits 24 of masking (forexample, with deposits of PMMA). Then a reactive ionic etching of thelayer made of GaAs is made (FIG. 6C). Finally, a deposit is made (FIG.6D) under a vacuum of a layer 25 of silver to form the electrodes 4 thena lift off which leads to the structure in FIG. 6E.

The selective etching of the GaAs layer on AlAs is obtained thanks tothe introduction of oxygen in the structure where the manufacture takesplace: when the GaAs is etched, a fine layer of oxide is formed on thesurface of the AlAs layer, it cuts down the etching speed considerablyand allows the etching to be stopped on this layer. This selectivity maybe generalised, for example, for InGaAs by introducing a layer ofInAlAs.

The value for the parameter h (FIG. 2), whose role is crucial inresonance, is then controlled at the time of the epitaxy, to withinabout a single layer (0.5 nm).

The metal deposit and lift-off stage may be replaced after having liftedoff the deposits 24 (see FIG. 6F) by a metal deposit and a damascene,that is to say a mechanical or mechanical-chemical polishing of themetal whilst respecting the elements 6. The arrow F in FIG. 6Frepresents the limit for this polishing.

In order to make the selectivity of the polishing easier, each one ofthe elements 6 may be made up by a semiconductor layer 6 a which absorbsthe light to be detected and on which a dielectric layer 6 b has beendeposited in advance. This dielectric layer 6 b may, for example, bemade of silicon nitride Si₃N₄, whose polishing speed is very slowcompared to that of metals, such as silver, which may be used. Thedielectric layer leading to the set of layers 6 b (and being used as alayer for stopping the polishing thanks to the great difference inhardness between the metal and the dielectric) may be deposited bysputtering after having made the absorbent semiconductor layer grow thatleads to the set of layers 6 a. Next, a mask is deposited, for example,made of nickel, which is used to protect the zones corresponding to theelements 6 during the course of the reactive ionic etchings in thedielectric layer (fluorous etchings, for example) then in the absorbentsemiconductor layer (chlorinated etchings, for example).

Should the metal deposit and the damascene work be carried out, twometal deposits 25 a and 25 b (see FIGS. 6G and 6H) with some sourcesinclined with respect to the substratum and using two different metals,allow the elements with two metals to be built (the case in FIG. 7).

The device that is the subject of the invention may be adapted to alarge range of wavelengths, ranging from visible to infrared (severalμm). On the other hand, it may be made with a large range ofsemiconductor materials.

It is possible to use different types of semiconductors in zone II (FIG.2), for example, under the form of heterostructures (epitaxial layers)to enhance the transportation of the charges and the device's speed.

The calculations have shown that a trapezoidal or partly rounded sectionof the electrodes does not fundamentally change the device'sfunctioning. On the other hand, the height h of the elements does playan important role.

Adding a dielectric layer to each element 6 does not modify the device'sfunctioning in a fundamental way either, but the respective heights ofthe different layers must be redefined and play an important role.

It is also possible to use some dissymmetrical electrodes in order tofavour the resonance on the most negative electrode and so to reduce thepath for the slow charge carriers (the holes in the example beingdescribed) with respect to the path for the fast charge carriers (theelectrons).

As has been seen, it is possible to use two different metals for theelectrodes, with two independent objectives. One is similar to thepreceding one and aims to favour the resonance on the most negativeelectrode whilst the other one aims to optimise the barrier heights foreach one of the two types of carriers and therefore reduce the darkcurrent.

The creation of carriers in the metal may take place for some photonswith a lower energy than the prohibited bandwidth of the semiconductorfor the elements 6 (larger wavelength), which increases the field forthe application of the invention.

Another device in accordance with the invention is shown in perspectiveon FIG. 7. The insulating layer and the Bragg mirror 8 are to be seenagain.

The elements 6 are seen as well. They are separated by electrodes eachof which, in the example being described, is in two adjacent parts 26and 28 which are respectively made of two different metals. It may beseen that an element 6 is contained between a part 26 and a part 28 andtherefore between two different metals.

On FIG. 7, the references 30 and 31 represent some waste from the layer22 at both ends of the device.

A cathode contact 32 and an anode contact 34 may be seen as well, whichare respectively in contact with the electrodes at the ends. This anodecontact and this cathode contact are linked to one another by means of aresistive element 36 that is in contact with each electrode and allowsthe potentials from these electrodes to be stabilised.

For the functioning of the device in FIG. 7, a voltage is appliedbetween the contacts, 32 and 34.

What is claimed is:
 1. Photodetection device configured to detect anincident light with a predefined wavelength, propagating in apropagation medium, comprising: an electrically insulating layer thatdoes not absorb the incident light; and at least one element, includinga semiconductor material and at least two biasing electrodes, formed onthe electrically insulating layer and configured to be carried torespective potentials that are different from one another, the at leasttwo biasing electrodes surrounding the at least one element, a setformed by the at least one element and the at least two biasingelectrodes configured to absorb the incident light, the at least oneelement and the at least two biasing electrodes having a shape that issubstantially parallelepipedal and extending following a same direction,dimensions of the at least two biasing electrodes and the at least oneelement, measured transversally to the same direction, being chosen, asa function of the predefined wavelength, to increase light intensity inthe set formed by the at least one element and the at least two biasingelectrodes, with respect to the incident light, making at least one oftwo modes resonate, including a first surface plasmon mode that is madeto resonate between interfaces that the set includes with an insulatinglayer and a propagation medium, resonance of the first mode taking placeat an interface between the at least one element and at least one of theat least two biasing electrodes, the first mode being excited by acomponent of a magnetic field associated with the incident light, acomponent that is parallel to the at least two biasing electrodes, and asecond transverse electrical mode of an optical wave guide perpendicularto the insulating layer and that includes the at least two biasingelectrodes, the second mode being excited by the component of theelectrical field associated with the incident light, and the componentis parallel to the at least two biasing electrodes.
 2. Device accordingto claim 1, wherein the surface plasmon mode is made to resonate and awidth of each of the at least one element, measured perpendicularly tothe same direction, is less than λ and higher than 0.02×λ, where λ is awavelength of the incident light and a thickness of each of the at leastone element is less than λ/(2n), where n is an average refractive indexfor each of the at least one element.
 3. Device according to claim 1,wherein the at least two biasing electrodes are made of a sameelectrically conductive material and are a same height, measuredpcrpendicularly to the insulating layer.
 4. Device according to claim 1,wherein the at least two biasing electrodes are at least one of (a) madeof different electrically conductive materials, or (b) have differentheights, measured perpendicularly to the insulating layer, in such a waythat the resonance takes place essentially on a side of the at least twobiasing electrodes that collect slow charge carriers at a time of thebiasing of the at least two biasing electrodes.
 5. Device according toclaim 1, wherein the at least one element includes a semiconductorheterostructure.
 6. Device according to claim 1, configured to detectincident light whose wavelength belongs to infrared range, wherein theat least two biasing electrodes are mainly made of Ag or Au to absorbthe incident light, and the at least one element not absorbing theincident light.
 7. Device according to claim 1, wherein the propagationmedium is air.
 8. Device according to claim 1, wherein the propagationmedium is a light guide parallel to the same direction along which theat least two biasing electrodes of each at least one element extends. 9.Device according to claim 1, including plural of the at least oneelement and electrodes that alternate on the insulating layer, with eachelectrode being made of a single metal or of two different metals. 10.Device according to claim 9, wherein the electrodes are configured to becarried to potentials that increase from one end electrode to anotherend electrode in a set of electrodes.
 11. Device according to claim 10,further comprising a resistive material, for stabilizing potentials, incontact with the electrodes and running from the one end electrode tothe other end electrode in the set of electrodes.
 12. Device accordingto claim 9, wherein the at least two biasing electrodes are configuredto be carried to potentials whose absolute values are equal and whosesigns alternate.
 13. Device according to claim 1, further comprisingmeans for reflection for reflecting light that is not absorbed, crossingthe insulating layer, with a thickness of the insulating layer beingchosen so that the light reflected by the means for reflection will bein phase with light waves present in the set formed by each at least oneelement and the at least two biasing electrodes and will participate inthe resonance.
 14. Device according to claim 13, configured to detectincident light whose wavelength is approximately 0.8 μm, the devicebeing formed on a substratum of GaAs, the at least one element beingmade of GaAs, the at least two biasing electrodes being made of Ag, theinsulating layer being made of AlAs, or out of an Al_(x)Ga_(1-x)material, with x being chosen such that this material will not absorbthe incident light but will allow a selective etching of the GaAs, andthe means for reflection being a multiple layer AlAs/AlGaAs mirror. 15.Device according to claim 13, configured to detect incident light whosewavelength is approximately 1.55 μm, the device being formed on asubstratum made of InP, the at least one element is made of InGaAs, theat least two biasing electrodes are made of Ag, the insulating layer ismade of AlInAs, and the means for reflection is a multiple layer mirrormade of GaInAsP/InP or AlGaInAs/AlInAs.
 16. Device according to claim13, configured to detect incident light whose wavelength isapproximately 1.55 μm, the device is formed on a substratum made ofGaAs, with the at least one element being made of an InGaAsNSb alloy,the at least two biasing electrodes are made of Ag, the insulating layeris made of AlAs, or in an Al_(x)Ga_(1-x)As material, with x being chosensuch that this material will not absorb the incident light but willallow a selective etching of the GaAs, and the means for reflection is amultiple layer GaAs/AlAs mirror.
 17. Procedure for manufacturing thephotodetection device according to claim 23, wherein a given thicknessof the semiconductor material of the at least one element is made togrow on the insulating layer, the semiconductor material is etchedselectively to remove portions in sites corresponding to the at leasttwo biasing electrodes and the at least two biasing electrodes areformed on the sites.
 18. Procedure according to claim 17, wherein a samemask is used to selectively etch the at least one element, then to formthe at least two biasing electrodes.
 19. Procedure according to claim17, wherein a same mask is used to selectively etch the at least oneelement, the mask is removed, the at least two biasing electrodes areformed using at least one metal, and excess material from this at leastone metal is removed by mechanical or mechanical-chemical polishing. 20.Procedure according to claim 19, wherein the excess material is removedby a selective mechanical or mechanical-chemical polishing of the atleast one metal with respect to the at least one element, with the atleast one element comprising a material whose hardness is greater thanthat of the at least one metal.
 21. Procedure according to claim 19,wherein the at least one element includes an upper layer and the excessmaterial is removed by a selective mechanical or mechanical-chemicalpolishing of the at least one metal with respect to the at least oneelement, with the upper layer of the at least one element comprising amaterial whose hardness is greater than that of the at least one metal.22. Procedure according to claim 19, wherein two metals are used to formthe at least two biasing electrodes, and are deposited successively inan oblique manner with respect to the insulating layer.